1. Field of the Invention
The present invention relates to an image forming apparatus using electrophotographic technique and relates in particular to an apparatus and method for forming an image using liquid developer composed of toner particles and solvent.
2. Description of the Related Art
There have been proposed wet-type image forming apparatuses having a heating means which is used in the developing process of the electrophotography to improve the quality of image.
In Japanese Patent Application Laid-open No. HEI 5-11566, an image forming apparatus is disclosed which is provided with a preheating roller located downstream from the developing unit and upstream from the transfer unit. The preheating roller is used to vaporize the solvent included in the developed image, which will causes the developed image to be prevented from spreading, resulting in improved quality of image.
However, excess solvent remains in the developed image from the developing unit to the preheating roller. Therefore, the excess solvent is likely to cause the spreading of the developed image, resulting in reduced quality of image. Further, it is necessary to provide space for the preheating roller. Therefore, the structure becomes complicated and its size becomes larger.
In Japanese Patent Application Laid-open No. SHO 58-143362, a squeezing apparatus is disclosed which is provided with a squeezing roller having a heater therein. Heating the squeezing roller to an appropriate temperature causes the viscosity of liquid developer to be reduced, resulting in improved effectiveness of squeeze.
In Japanese Patent Application Laid-open No. HEI 9-101683, a wet-type electrophotographic copying machine is disclosed which is provided with a developing unit having a heating element therein. The heating element heats the liquid developer to an appropriate temperature ranging from 50 to 60 degrees Celsius to prevent the toner particles of the liquid developer from agglomerating.
However, neither the squeezing roller having a heater therein nor the developing unit having a heating element therein as described above provides a means for effectively removing excess solvent from the developed image. Therefore, the excess solvent is likely to cause the spreading of the developed image, resulting in reduced quality of image.